Vapor Phase Ammonolysis of ε-Caprolactone over Copper Solid Acid Catalysts

Abstract

The vapor phase ammonolysis of e-caprolactone to obtain e-caprolactam over copper-solid acid catalysts was investigated to elucidate the reaction mechanism. The reaction was carried out in a flow type under atmospheric pressure. The products obtained were e-caprolactam, 6-hydroxyhexanenitrile, 6-hydroxyhexanamide, adiponitrile and polymers; their yields were dependent on the catalysts and reaction conditions. With solid acid catalysts 6-hydroxyhexanenitrile was formed and copper scarcely showed a catalytic activity toward e-caprolactone. When the binary copper-solid acid catalysts were reduced before use and employed in the presence of hydrogen, e-caprolactam was mainly obtained; but otherwise, the main product was 6-hydroxyhexanenitrile. In the case of copper-titania catalyst, e-caprolactam was obtained in the maximum yield at 260-270°C. The catalytic activity decreased rapidly with time on stream, probably due to the covering of the catalyst surface with polymer. The addition of water to the feed increased the yield of e-caprolactam. The obtained results suggested the following reaction pathway: e-Caprolactone reacted with ammonia over solid acid to convert it into 6-hydroxyhexanamide, which was then dehydrated to form e-caprolactam over reduced copper. In the absence of copper, the intermediate was dehydrated to form 6-hydroxyhexanenitrile over solid acid.